DC voltage conversion circuits are useful in many applications. For example, an electronic product may receive a first DC voltage externally, but be designed to use a second, different DC voltage internally, and therefore need to convert between the two. Different types of DC voltage converters exist. A boost converter receives an input voltage and produces an output voltage having a magnitude greater than that of the input voltage. Conversely, a buck converter produces an output voltage having a magnitude less than that of the input voltage.
A buck-boost converter can produce an output voltage magnitude that is either greater than or less than an input voltage magnitude. Buck-boost converters can be useful in battery-powered electronic products. Circuits in such products may be designed to use a predetermined supply-voltage magnitude range. When the battery is fresh, it may supply a voltage magnitude higher than the predetermined range, and when the battery is more depleted, it may supply a voltage magnitude lower than the range. Thus, both buck and boost conversion is needed.
One problem with buck-boost converters is that it is difficult to implement an efficient and simple control scheme for dividing the operation of the buck-boost converter between regimes of pure buck operation (buck mode), pure boost operation (boost mode), and mixed buck-boost operation (buck-boost mode).